class_docstr: A helper class that represents input string that to be modified.
  
  Text that Sample contains parsed in data set,
  ``TextField`` provides multiple methods for Sample to modify.
  
  Support sentence level and word level modification,
  default using word level API.
code: def set_mask(self, index, value):
      if not self._mask:
          self._mask = [ORIGIN] * len(self.words)
  
      if index > len(self.mask) - 1:
          raise ValueError(
              "Index {0} out of range {1}".format(
                  index, len(self.mask) - 1
              )
          )
      if value not in [ORIGIN, TASK_MASK, MODIFIED_MASK]:
          raise ValueError(
              "Support mask value in {0},  while input mask value is {1}!".format(
                  [ORIGIN, TASK_MASK, MODIFIED_MASK], value
              )
          )
      self._mask[index] = value
  
imports: from .field import Field
  from ....common.utils.list_op import *
  from ....common.preprocess.en_processor import EnProcessor
  from ....common.settings import ORIGIN, TASK_MASK, MODIFIED_MASK
label_desc: Use image node_id 5 for calling the TextField obj's underlying member method code with example usage: obj.set_mask(index, value) without return types